The present invention relates to a protective packaging or reinforcement assembly for packaging the spliced portions of optical fibers, and to a protective packaging method for protecting and reinforcing the spliced portions by the use of such a protective packaging assembly.
One of the most practical and reliable methods for optical fiber splicing is fusion splicing, comprising the steps of stripping the plastic coatings from the two fiber ends to be spliced, placing the two bare fiber ends in an end-to-end position, and of fusion splicing, such as arc splicing the bare fiber ends by a process such as arc fusion. However, this fusion splicing method needs a subsequent packaging process for protecting the completed splice since the splice has no protective coating.
Several protective packaging methods of reinforcing the spliced portion of an optical fiber have heretofore been proposed, which include those methods using a heat-shrinkable tube, such as disclosed in Japanese Patent Application Laid-Open Specification No. 129,305/1980 and in "Fusion Splicing of Optical Fibers", by J. F. Balgleish, Electronics Letter, Vol. 15, No. 1, p. 32(1979). In the prior art methods using a heat-shrinkable tube, an external heating source or device such as an electric heater must be employed to shrink the heat-shrinkable tube. Therefore, such an external heating device must be carried, for example, into a manhole or up to the top of a pole for in the field optical fiber splicing. The packaging process requires a relatively long heating time, i.e., 2-3 minutes, because the protective packaging assembly is externally heated from the outside by an external heat source. With respect to the packaging materials, the Young's moduli of the heat-shrinkable tube and any hot-melt adhesive are in the order of 1-100 kg/mm.sup.2, which are much lower than the Young's modulus of an optical fiber, i.e. approximately 7,000 kg/mm.sup.2. This creates a concern that the optical fiber will be broken when a tensile stress is applied to the reinforced portion of the optical fiber to elongate the packaging materials so that a breaking stress may be put on the optical fiber. Furthermore, the linear expansion coefficients of the heat-shrinkable tube and any hot-melt adhesive such as the packaging materials are in the order of 10.sup.-5 to 10.sup.-4 /.degree.C., which are higher than the linear expansion coefficient of the fused silica optical fiber, which is in the order of 10.sup.-7 to 10.sup.-6 /.degree.C. This leads to such a disadvantage that, owing to the expansion or contraction, upon temperature change, of the above-mentioned plastic packaging materials, transmission loss increase of the optical fiber due to microbending thereof and/or fiber breaking caused by protrusion of the optical fiber are liable to occur.